你可能想玩转 aggregate

例如:

aggregate(DF$mw3wuus, FUN=mean, 
          by=list(y1=DF$y1, y0=DF$y0, y3=DF$y3, y4=DF$y4))

会给你:

  y1 y0   y3 y4    x
1 AG  2 1994 AA 45.5
2 AI  1 1997 AA 22.0
3 AI  1 1994 EB 78.0
4 AI  1 1999 EB 21.0
5 AG  2 1996 FB 34.0